The present invention relates in general to programmable measuring and more particularly concerns novel apparatus and techniques for rapidly and automatically testing the transmission characteristics of a communications channel that may be remote from a central computer through measuring analog test signals transmitted over the channel while communications between the central computer and the terminal points of the channel under test are through reliable digital signals to enable the digital computer to readily determine the transmission characteristics of the communications channel under test.
A typical prior approach to checking a communications channel comprises a local computer in a closed loop including the communications channel to be tested. Having a digital computer for each communications link is costly, for a typical communications system has many links.
Accordingly, it is an important object of this invention to provide apparatus and techniques that facilitates using one digital computer to automatically measure transmission characteristics of a number of communication links in a communications system.
It is a further object of the invention to achieve one or more of the preceding objects with programmable local units that are relatively inexpensive and reliable.
It is a further object of the invention to achieve one or more of the preceding objects with programmable local units characterized by a high degree of flexibility and capable of functioning both to receive and transmit test signal waveforms and to accept digital command signals from the computer and provide digital signals to the computer relevant to the programmable measurements being made.
It is a further object of the invention to provide novel apparatus and techniques for providing a wide variety of waveforms.
It is a further object of the invention to provide a programmable local unit having both a digital signal input and a digital signal output for communication with a digital computer and an analog input and analog output for exchanging signals with a communication link to be tested.
It is still a further object of the invention to provide novel shift register techniques for generating analog waveforms.
It is still a further object of the invention to provide shift register techniques for converting a received analog signal into corresponding digital signals.
It is still a further object of the invention to achieve one or more of the preceding objects while controlling signal gain to keep signal levels so as to obtain substantially maximum resolution.